Resource Allocation of MU-OFDM Based Cognitive Radio Systems Under Partial Channel State Information

For wireless transmission, the assumption that the transmitter always obtains the channel state information (CSI) is unreasonable because of feedback delays, estimation error and quantization error. When the transmitter can't receive the channel state information perfectly, the performance of the wireless systems will degrade. Some prescribed quality of service (QoS) requirements will not be satisfied. In order to avoid the system's degradation, a more concrete analysis of wireless transmission under imperfect CSI is needed. Cognitive Radio (CR) is a promising technique for improving the spectrum efficiency in future wireless network. In this paper, the downlink transmission based on partial channel state information due to feedback delays in a multiuser Orthogonal Frequency Division Modulation (MU-OFDM) based CR system is investigated. We analyze the impact of partial channel state information on the wireless transmission. A new transmission schedule is derived based on obtained partial CSI. Simulation results show that the new transmission schedule satisfies the given QoS while achieving high data rate. The more the partial CSI is correlated to the real CSI, the higher data rate is achieved.